The 3rd Generation Partnership Project (3GPP) includes a work item known as Long term Evolution (LTE) to improve the Universal Mobile Telecommunications System (UMTS) standard in response to increased demand for mobile data services. Multimedia Broadcast and Multicast service (MBMS) is one service offered in the UMTS standard. MBMS is a broadcast service similar to conventional television and radio broadcast systems in which the same content is transmitted to multiple users located in a specific service area, referred to herein as the broadcast service area. Mobile TV, a service that enables mobile terminals to receive ordinary television programs, is one example of a MBMS.
Two different scenarios are contemplated for providing MBMS: single cell transmission and MBMS Single Frequency Network (MBSFN). With single cell transmission, the broadcast content is transmitted to the user from a single cell and a user may be handed over as it moves from one cell to another. In MBSFN, multiple transmitters in different cells transmit the same broadcast service synchronously using the same radio resources. There is no need for the network to handover the user as the user moves between cells within the MBSFN service area. Outside the MBSFN service area, the mobile terminal receives the broadcast service from a single cell.
In general, MBSFN may be preferable in service areas where there are many users. MBSFN provides an efficient way of providing services to a large user population that is dispersed over a wide area. On the other hand, single cell transmission may be preferred in service areas where there are a small number of users or the user density is low. Consequently, a broadcast service area may include both MBSFN service areas and non-MBSFN cells.
When a mobile terminal is operating within an MBSFN service area, the mobility of the mobile terminal will typically not be an issue because the broadcast service will be provided by all cells within the MBSFN service area. There is no need for the network to track the mobility of the mobile terminal in order to provide the broadcast service. However, when the mobile terminal moves from an MBSFN service area to a non-MBSFN cell, the broadcast service may be interrupted or lost unless the mobile terminal can receive the broadcast service in the non-MBSFN cell. If the mobile terminal is operating in a receive-only mode, the network may not know the exact location of the mobile terminal and thus may not be aware when the mobile terminal is approaching a boundary of the MBSFN service area. Therefore, some mechanism is needed in order to maintain continuity of broadcast services as the mobile terminal moves between an MBSFN service area and a non-MBSFN cell.